1. Field of the Invention
The present invention relates generally to fluid medicament dispensers. More particularly, the invention concerns a novel patient controlled fluid dispenser for use in sequentially dispensing doses of a liquid medicament of predetermined volume at predetermined intervals.
2. Discussion of the Prior Art
In recent years considerable research has been directed toward the development of an apparatus that enables patients to safely administer doses of intravenous medication at will without the need for constant supervision by medical staff. In this connection, as early as the 1960s researchers began testing an apparatus that would allow patients to self-administer doses of opioid drugs when they felt the need for them. The early patient controlled analgesia (PCA) devices typically comprised electromechanical devices such as electronically controlled infusion pumps which were connected to a timing device. In using these devices, when the patients experienced pain, they triggered the device by depressing a button located at the end of a cord extending from the machine. The machine then delivered a preset amount of an analgesia drug into the patients in-dwelling IV catheter. A timer was programmed to preclude administration of additional doses until a specific interval of time had elapsed, a so-called lockout or delay interval. The purpose of the lockout interval was to prevent the patient from administering a second dose until after the first dose had time to exert its maximal effect.
In addition to the early electromechanical type prior art devices, a number of mechanical devices were also proposed. These mechanical devices usually prevented overdosing through the use of a flow restrictor of some kind so that, even if the patient were to actuate the apparatus repeatedly at short intervals, the restrictor would prevent the safe overall dose level from being exceeded. Accordingly, such devices permitted the patient to administer low doses of medication at frequent intervals and, therefore, was an almost continuous administration of drugs. With some medication, this can be an advantage, with other medications, it can create significant problems. With medications, such as analgesia, it is preferable that the doses be less frequent and in larger volumes.
Even using the somewhat primitive early prior art PCA devices, it was clearly established that the effectiveness of the administration of analgesia is significantly enhanced when the medicine used can be controlled by the patient, rather than being administered by a standard procedure involving a caregiver each time the medicament is needed. The enhancement is manifested in several ways, including improvements to the patient's comfort, minimization of any adverse side effects related to the amount of medication used and minimizing the time required by nurses and other care givers. Additionally, with patient controlled administration, experience has shown considerably less medicine is required to achieve the specific levels of pain relief desired.
In recent years PCA has been used widely to improve the quality of postoperative pain management. The PCA approach advantageously allows the patient to take as much analgesic as necessary to achieve satisfactory relief of pain, thus overcoming variation among individuals in analgesic requirements. It also avoids problems of administration of analgesia caused by staff shortages in hospital wards. Additionally, a rational use of a PCA-infusion device allows the individual patient to overcome variations in pharmacokinetic and pharmacodynamic factors by titrating the rate of narcotic administration to meet their analgesic needs. If recurrent nausea or vomiting develops after bolus injections, the patient can be switched to a different narcotic analgesic or the PCA therapy can be discontinued.
PCA therapy is ideally suited for certain types of treatment where pain is intermittent. For example, patients with chronic cancer pain often have periods in which there is minimal discomfort and, during that time, analgesia is not required. Therefore, a patient may use less total drug than if administered by continuous infusion. Second, continuous intravenous morphine infusion results in narcotic tolerance, necessitating dose escalations to provide consistent pain relief Because less narcotic may be given by patient-controlled analgesia, the development of tolerance may prove to be less than that produced by continuous intravenous morphine infusions.
Exemplary of the prior art electromechanical type devices for infusing analgesia and like medications to a patient on demand is the apparatus disclosed in U.S. Pat. No. 5,069,668 issued to Boyd. One form of mechanical type, patient controlled analgesia infusion apparatus is described in U.S. Pat. No. 5,135,491 issued to Baldwin. This latter patent discloses an apparatus in which the liquid to be self administered by the patient is controllably supplied from a positively pressurized supply reservoir to a lower pressure dose chamber of a patient operable syringe from which the patient may expel the liquid to be used into a suitable infusion site such as an in-dwelling cannula. The supply of liquid from the reservoir into the dose chamber is controlled by a flow control metering tube assembly which provides a selected flow rate for a reference of fluid and a reference of pressure differential.
Exemplary of another type of prior art mechanical PCA apparatus is the apparatus disclosed in U.S. Pat. No. 4,828,551 issued to Gertber et al. This apparatus, which is mechanical/hydraulic in nature, comprises a reservoir and a pump operable by the patient for dispensing medicine from the reservoir into the patient's IV system in incremental doses. The pump capacity per stroke may be adjustable, thereby adjusting the size of each dose dispensed. Timing apparatus assures that a specific interval of time must pass between sequential dosage dispensations.
The thrust of the present invention is to provide a vastly improved, compact, readily portable and easy-to-use, patient-controlled fluid dispenser for use in controllably dispensing fluid medication at a selected uniform rate. More particularly, a primary object of the invention is to provide a device of such a character which is of an all mechanical construction that is ideally suited for patient administration of pain killing drugs in a home environment. The devices of the invention are uniquely configured so that the treating physician can preset the volume of each of the multiple doses to be self-administered by the patient and can also preset, and precisely control the intervals at which the doses can be given.